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Post by 2twisty on Jun 2, 2014 23:49:01 GMT -5
I have a Roketa 250B, VOG 260/Linhai clone engine.
Recently, I noticed a real lack of power and acceleration. I finally diagnosed it as the carb slide was not moving properly. If I open the seat and tap on the cover for the diaphragm, it works fine for a few minutes and then gets stuck again. Sometimes it will stick and unstick all on its own.
If I stop the engine in the "stuck" state and remove the diaphragm cover, I have to apply a moderate amount of force to get the diaphragm and needle to come out of the carb. I can immediately reinsert it and it slides like it's glass. I am unable to get it to stick when manipulating it.
When it works, it works great. When it fails, it's like someone snuck into my garage and replaced the 250cc engine with a 150.
Apart from just replacing the carb, what can I do? I'd rather fix it than just throw parts at it.
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Post by alleyoop on Jun 3, 2014 0:24:38 GMT -5
Take the diaphragm out and check the needle it may be bent a little bit and is sticking in the defuser. Also the needle should move some hanging there. Did you by chance change the main jet in the carb? Did you ever take the top off maybe you do not have the spring installed right it fits around a protroding piece on the inside of the cap. Also if you took it off to clean did you maybe install the needle guide backward.
One other thing if it is staying down sometimes or when it works sometimes does it loose power if so check then the rubber part is leaking and dropping the needle. Some get rips and some even pin holes some also leak around the center where the rubber is held in place and seal.
Alleyoop
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Post by rockynv on Jun 3, 2014 3:35:57 GMT -5
Also how clean is the groove or bore that the slide rides in? If it got carboned up and galled a bit it may need cleaning and smoothing afterwards with some crocus cloth.
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Post by 2twisty on Jun 3, 2014 9:22:48 GMT -5
I don't think it's the diaphragm. This is because it's physically stuck. Once I free it, I can't for the life of me make it do anything slide like it's on greased snot. It feels great -- perfect, actually, until I reassemble and it works for a while.
I am certain that I'm installing the spring correctly. I've never disassembled the slide/diaphragm/needle assembly, so it can't be that I put it together wrong.
My next step was to remove the needle and check to see that it's not bent. However, I would expect that I could feel it binding if it were. I was hoping to find a way to fix this without removing the carb, since I can't see a way to remove it easily without taking lots of plastics off.
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Post by rockynv on Jun 3, 2014 12:31:47 GMT -5
I am getting a bit confused here. If you have disassembled it to the point that you are removing and reinstalling the spring, manually movinge the slide afterwards, then you just need to lift the diaphragm (disengaging it from its groove first) removing it with the slide and needle from the carb.
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Post by alleyoop on Jun 3, 2014 12:44:50 GMT -5
You do not have to take the carb off just Take the two screws off the top and pull the diaphgram out with needle and all. alleyoop    |
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Post by richardthescooter1 on Jun 3, 2014 14:14:19 GMT -5
Sometimes they are tricky putting back in, never force it, have patience, make sure the rubber lines up where the tab goes in on the diaphragm.
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Post by 2twisty on Jun 3, 2014 15:48:43 GMT -5
yes, I am doing all that. I can't manage to make it stick unless I am riding the bike. if I wanted to smooth the bore in the carb, what would I use? steel wool? 1500 grit wet?
How can I tell whether the sticking is from the needle or from the slide?
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Post by richardthescooter1 on Jun 3, 2014 15:56:19 GMT -5
If you have the needle in hole and diaphragm in right and spring in and cap and tighten down, it should be working fine.
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Post by richardthescooter1 on Jun 3, 2014 17:57:27 GMT -5
I'd check the ACV Valve which need vacuum to work probably, maybe the problem is there?
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Post by alleyoop on Jun 3, 2014 19:03:06 GMT -5
ACV Valve has nothing to do with the Slide and diaphgram.
Take the Diaphgram completely out and check the slide for scrap marks. May want to take some pictures of it out and check if the needle is straight.
Also hold the rubber up to the light and see if you can see any pinholes or little tiny rips.
Alleyoop
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Post by 2twisty on Jun 3, 2014 22:12:14 GMT -5
There is some small amount of scrape marks at the bottom of the slide. However, the slide moves very smoothly in the bore. In fact, I have tried every way I can think of to make this thing stick. I'm wondering if something has happened to the emulsion tube...
I removed the needle and examined it carefully. It's smooth through its entire length and is not bent. The diaphragm has no holes or cracks and is quite supple.
Do any of you know what this carb is a copy of? If I wanted to order a rebuild kit for it, what would I look for?
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Post by 2twisty on Jun 3, 2014 22:28:37 GMT -5
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Post by alleyoop on Jun 3, 2014 22:33:29 GMT -5
Yep, if you cannot find what is causing it to stick then your best bet is just replace it.
Alleyoop
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Post by richardthescooter1 on Jun 4, 2014 6:55:16 GMT -5
Thanks alleyoop, just thought that maybe the problem was coming from a different part of carb.
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..BAD TO THE BONE..
